This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-177061 filed on Jun. 13, 2000, the entire content of which is incorporated herein by reference.
The present invention generally relates to a bar antenna used to receive radio waves. More particularly, the present invention pertains to a bar antenna positionable at a variety of different places on a vehicle, including the vehicle door handle or the vehicle door mirror, or on portions of a house such as the door, for receiving radio waves, and a method of manufacturing a bar antenna.
Somewhat recent developments have led to electric key-less entry systems for homes and electric key-less entry systems for vehicles. According to these electric entry systems, as soon as the person carrying the electric key for the entry system touches, for example, the door knob, the system unlocks the entry system. With this type of entry system, an antenna must be placed within two or three meters of the entry system.
Generally speaking, a bar type antenna is utilized and is made from ferrite material having high magnetic permeability. One example of such material is high magnetism ceramic material. This known type of bar antenna formed from ceramic material is susceptible of certain disadvantages and drawbacks in that the antenna tends to be relatively fragile.
The material quality of the core placed in the antenna will deteriorate over time. If a small amount of shock or vibration is applied to the core for a relatively extended time, it is difficult to prevent the formation of a crack on the core. The crack shortens the actual length of the antenna and deteriorates the response of the entry system.
One suggestion proposed in Japanese Patent Laid-Open Publication No. 9-307327 involves constructing the ferrite bar-type antenna to possess sufficient strength. The published application describes connecting a plurality of ferrite cores in an aligned manner and placing the ferrite cores into a tube while winding a coil on the outer surface of the tube. According to this structure, a core having the appropriate length is put into the tube to prevent the formation of a crack.
However, with this bar antenna, gaps exist between the cores, thus reducing the sensitivity of the antenna as compared to an antenna having a core defined by single structure. Moreover, the gaps cause the connection between each of the cores to be relatively unstable. This also reduces the responsiveness and reliability of the antenna performance.
In light of the foregoing, a need exists for a bar antenna having a stable receiving capacity and stable performance, while at the same time not being as susceptible to the possibility of damage to the same extent as the other known antenna""s described above.
According to one aspect of the invention, a bar antenna includes a single body ferromagnetic substance core, a bobbin accommodating the core and having at least one coil outside of the bobbin, a case in which is positioned the core and the bobbin, and a potting material between the core and the bobbin.
According to another aspect of the invention, a method for manufacturing a bar antenna involves winding a plurality of coils onto a bobbin, placing a single body ferromagnetic substance core into a hollow space of the bobbin, positioning the bobbin in a case, and introducing a potting material into the hollow space of the bobbin.
Another aspect of the invention involves a bar antenna in combination with a portion of a vehicle. A case is mounted on a mounting surface of the portion of the vehicle, a bobbin is positioned in the case and has a hollow space, a one-piece ferromagnetic core is positioned in the bobbin, at least one coil winding is wound around the outside of the bobbin, and a potting material is located between the bobbin and the case, and between the core and the bobbin.
In accordance with the present invention, the core is insulated from temperature change, humidity change and shock or vibration by virtue of the potting material. The potting material positions the core generally at the center of the bobbin and affixes or secures the core and the bobbin together.